1. Field of the Invention
The present invention relates to a roll, particularly a back-up roll, for rolling flat material. The roll is composed of a rotating roll shell and means arranged within the roll shell for influencing the bending stiffness of the roll shell.
2. Description of the Related Art
During the rolling process the rolling forces are applied by work rolls which rest on the flat material, for example, metal strip. The rolling forces must be distributed as uniformly as possible over the entire length of the roll, i.e., the line of contact between the circumference of the roll and the strip should be a straight line. The rolling stock interferes with obtaining the straight line, and this interference results in a zone of the roll to which a greater load is applied and in a crown of the roll.
In order to prevent this, back-up rolls are usually placed on the work rolls, wherein the back-up rolls must have a sufficient bending stiffness. In addition, in order to prevent the crown, systems are known in the art which change through hydraulic mechanisms the crown of a roll and in individual cases also the width of contact. In these systems, the crown and possibly also the resiliency of the roll relative to external loads along the crown are influenced by means of oil pressure cushions and/or hydraulically actuated support shoes and are adapted to the rolling conditions. Disadvantages of these systems are the sometimes very complicated high-pressure hydraulic units as well as problems with respect to tightness which result in contamination of the rolling oil or emulsion by the hydraulic oil. Moreover, the applications are limited by the structural size, so that these systems at the present time can be used exclusively as back-up rolls.
In addition, systems with displaceable rolls are known in the art for influencing the flatness and the profile during rolling of metal strip. In these systems, either the load distribution between the rolls is adjusted by a partial displacement of at least two rolls or the roll gap is influenced. In accordance with the continuous variable crown method (CVC-method), it is proposed to react to the formation of crowns of rolls by displacing suitably contoured rolls relative to each other.
It is also known in the art to use shell-type rolls as backup rolls which have a high bending stiffness in spite of their hollow interior. In this connection, German patent application 196 37 584.3 proposes to compensate bending of the shell-type rolls by means of friction bearings within the rolls. These friction bearings are, for example, spherical friction bearings mounted on a support axis or shaft, wherein the friction bearings can be arranged so as to be adjustable with respect to their spacing and securable in their position. The friction bearings are constructed as oil film bearings. However, the rolls of this type have the disadvantage that the compensation zone between the bearing shells in the interior of the roll and the shell of the back-up roll is predetermined by the respective bearing width, number of bearings and arrangement of bearings. Consequently, this system cannot operate without additional adjusting means for influencing the flatness.
U.S. Pat. No. 4,407,151 also proposes the mounting of support means in the hollow interior of a shell-type roll as a possibility for influencing the bending stiffness of the roll. For example, support discs mounted on a shaft are to be arranged at selected points along the length of the roll. The discs themselves can be displaced along the hollow interior of the roll by applying pressure. In addition, it is proposed that the roll shell receives a shaft with clearance fit or close fit. The adjustment to the flat material to be processed is achieved by displacing the respective shafts of two back-up rolls.